The present invention relates to a laminate printed circuit board and a method of producing the same and, more particularly, to a laminate printed circuit board loaded with transistors, ICs (Integrated Circuits), LSIs (Large Scale Integrated Circuits) or similar circuit devices, and a method of producing the same.
The problem with a laminate printed circuit board of the type described is that the circuit board generates electromagnetic noise and causes an electronic equipment including it or other electronic equipments to malfunction, as well known in the art. The electronic noise is ascribable to radiations caused by currents derived from the parasitic capacitance and parasitic mutual inductance of the circuit and high frequency currents flowing into a power supply line. These causes are generally referred to as a common mode. Because the mechanism causing such radiations occur are complicated, implementations for coping with the above problem at positions adjoining the sources of radiations have not been available except for a metallic casing for electromagnetic shielding. The metallic casing accommodates the entire electronic equipment therein.
It is a common practice with a laminate printed circuit board to connect ICs/LSIs, which are the sources of high frequency power supply currents, between a power supply line implemented by a power supply layer and a ground line implemented by a ground layer. Decoupling capacitors are connected in parallel, each in the vicinity of the respective IC/LSI. The power supply layer is a full flat layer entirely constituted by a conductive film. With this configuration, the power supply layer maximizes the area over which a current flows and thereby reduces the resistance of the power supply line, i.e., the variation of a DC power supply voltage.
The above conventional laminate printed circuit board has a problem that the designer cannot control the high frequency power supply currents to flow into the power supply layer due to the switching operation of the IC/LSIs. Specifically, the impedance of the full flat power supply layer is so small, a high frequency power supply current output from one IC/LSI flows not only into the decoupling capacitor adjoining it but into the other decoupling capacitors. As a result, the distribution of the high frequency power supply currents in the entire printed circuit board is too complicated to be analyzed with ease. It has therefore been impracticable to determine the capacity of the individual decoupling capacitor IC/LSI by IC/LSI. Moreover, the high frequency power supply currents flown into the power supply layer follow complicated paths due to the full flat configuration of the power supply layer. Consequently, such currents sometimes form large loops which would aggravate the electromagnetic noise and immunity. Although the entire electronic equipment may be housed in a metallic casing, as stated earlier, it is difficult to fully obviate the leakage of electromagnetic noise to the outside of the casing because the casing must be formed with an opening for arranging, e.g., an operation panel.
Technologies relating to the present invention are also taught in, e.g., Japanese Patent Laid-Open Publication Nos. 6-61602, 2-21700 and 6-244582, Japanese Utility Model Laid-Open Publication No. 4-43016, Japanese Patent Laid-Open Publication Nos. 3-273699, 3-208391, 64-25497 and 63-300593, Japanese Utility Model Laid-Open Publication Nos. 61-173167 and 61-38970, and Japanese Patent Laid-Open Publication Nos. 5-235679, 4-302498 and 4-3489.